Vehicle provided with a fluidic accelerometer

ABSTRACT

A fluidic device senses acceleration of a vehicle or the like and may control a fluid motor or other mechanism which is to be actuated in response to acceleration. A nozzle directs a jet of fluid across an open gap in a direction transverse to the direction along which acceleration is to be sensed. Two receiver ports are positioned to receive and divide the fluid jet in the absence of flow deflection. Upon acceleration of the device, inertial effects cause the jet flow to be slightly deflected thereby changing the amount of flow received at one receiver port relative to the other to produce a fluidic signal. The signal may be amplified and caused to actuate a fluid motor. Compensating means are provided to eliminate signal error which might otherwise arise from tilting of the device or from changes in jet fluid viscosity.

This is a division of Ser. No. 437,205, filed Jan. 28, 1974.

BACKGROUND OF THE INVENTION

This invention relates to instruments for detecting acceleration and forproducing signals in response thereto.

In various vehicles, as well as in other contexts, an instrument may beneeded for sensing acceleration in one or more directions and forproducing signals indicative of acceleration. Such an instrument may beused to activate some mechanism which is to be operated while acondition of acceleration exists. Considering a specific example,vehicles designed to travel over rough or uneven terrain often havewheels attached to the vehicle frame through resilient suspensionsystems to allow a wheel to travel over an obstacle without the upwardmotion being fully transmitted to the vehicle frame. This shockabsorbing effect can be enhanced if a fluid cylinder is connectedbetween the wheel and frame and if means are provided for sensing thevertical acceleration which accompanies passage of the wheel over anobstacle. The acceleration signal can be caused to actuate the fluidcylinder to forcibly lift the wheel relative to the frame enablingoverriding of the obstacle with reduced upward movement of the frameitself. In other instances, typically found in earthworking vehicles,the operator's seat may have a fluid suspension in which fluid pressureis momentarily varied when upward or downward acceleration of thevehicle is sensed in order to reduce jarring of the operator whentraveling over rough terrain. Many other forms of apparatus are known inwhich it is necessary to sense acceleration and to actuate somemechanism in response thereto.

The acceleration sensors heretofore employed for such purposes typicallyinclude a mass or weight suspended or supported by spring means. Due toinertial effects, any sudden acceleration of the structure surroundingthe weight is accompanied by a lag in the movement of the weight itself.This relative movement between the surrounding structure and the weightis caused to actuate a slide valve which controls a fluid flow that inturn actuates a fluid motor or some other mechanism. Accelerometers ofthis kind are subject to the several difficulties inherent in the use ofmechanical mechanism for performing sensitive detection functions. Suchdevices are necessarily bulky and are costly if manufactured to exhibitmaximum precision. Sensitivity is limited by the friction between movingparts and there is a considerable risk of malfunctions from seizing,wearing and breakage of mechanical elements. Further, spring masssystems have inherent resonances which result in poor frequencyresponse. In other words, a given spring mass system will oscillate muchmore strongly in response to acceleration at one particular rate or atharmonics thereof while being much less sensitive to acceleration atother rates.

To avoid the problems of mechanical accelerometers, fluidic devices haveheretofore been designed in which acceleration is sensed from thedeflection of a jet of fluid traveling across an open gap between anozzle and one or more receiver ports. Jet deflection from accelerationcauses pressure and flow changes at the receiver ports which aredetected and amplified by fluidic circuit elements. As heretoforeconstructed, fluidic accelerometers have been subject to signal errorfrom certain causes. For example, if such devices are operated in atilted condition, gravitational deflection of the jet is changed with aresultant change in the output signal similar to what is produced byacceleration. Changes in the viscosity of the jet fluid from temperaturechanges may also cause an erroneous output signal by altering jetvelocity and thereby altering gravitational drop of the jet in passageacross the gap.

SUMMARY OF THE INVENTION

This invention is a highly accurate fluidic system for producing signalsin response to acceleration. In particular, the system includes meansinherently compensating for error which might otherwise result fromtilting of the device or from fluid viscosity changes.

In one form of the invention, a fluid flow receiver has a pair ofreceiver ports with centers which are spaced apart in the directionalong which acceleration is to be sensed. A nozzle directs a jet offluid under pressure across an open gap and is positioned whereby theflow is divided between the two receiver ports in a predetermined ratioin the absence of acceleration. Upon acceleration, inertial effectscause the flow across the open gap to be deflected at least momentarilythereby altering the normal flow division between the two receiver portsto produce the desired acceleration signal.

Compensation for changes in gravitational deflection of the jet, as aresult of inclination of the device or viscosity variation, is providedfor by a valve situated between the jet nozzle and a source of fluid atconstant pressure. The compensation valve is controlled by feedback ofthe output signal of the accelerometer to adjust jet flow to restore theoutput signal to a predetermined value if a slow change in the outputsignal occurs. Relatively fast changes in the output signal, which arisefrom acceleration rather than other causes, do not significantly shiftthe compensator valve.

In one form of the invention, the flow differential signal from thereceiver ports that indicates acceleration is fluidically amplified andcaused to pilot a valve which in turn controls mechanism, such as afluid cylinder in a vehicle wheel suspension, which is to be actuated inresponse to acceleration.

Accordingly, it is an object of this invention to provide a more preciseand reliable fluidic accelerometer for detecting acceleration and forproducing a signal in response thereto.

The invention, together with further objects and advantages, thereof,will best be understood by reference to the folowing description of apreferred embodiment taken in conjunction with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a section view of a fluidic acceleration sensing devicetogether with other fluid circuit elements for controlling a fluid motorin a vehicle suspension wherein certain of the fluid circuit elementsare shown schematically,

FIG. 2 is a foreshortened enlarged section view of the accelerationsensing device of FIG. 1, and

FIG. 3 is a view taken along line III--III of FIG. 2 further clarifyingthe relationship of certain fluid ports illustrated therein.

DESCRIPTION OF A PREFERRED EMBODIMENT

Referring initially to FIG. 1 of the drawing, an acceleration sensingdevice 11 in accordance with the invention may have a support means orbase 12 which in this particular example has a broad U-shapedconfiguration consisting of a flat floor 13 with an upstanding nozzleendwall 14 at one end and an upstanding receiver endwall 16 at the otherend. In this particular example, it is desired to sense acceleration ina vertical direction, both upwardly and downwardly, and accordingly, thedevice 11 is disposed with the floor 13 extending in a horizontal plane.

Referring now to FIGS. 2 and 3 in conjunction, upper and lower receiverports 17 and 18 respectively are situated at the inner face of receiverendwall 16, the two receiver ports being circular in this example andbeing tangent to each other at the inner surface of the endwall. Astepped upper output passage 19 extends through endwall 16 to connectwith upper port 17 while a stepped lower output passage 21 extendsthrough the endwall to connect with lower port 18, the passages 19 and21 being divergent within the endwall.

A nozzle element 22 having a jet forming flow orifice 23 is disposed atthe inner surface of the opposite endwall 14. A passage 24 for receivingpressurized fluid extends through the endwall 14 to communicate with thenozzle orifice 23. Nozzle orifice 23 may have a diameter substantiallyequivalent to that of an individual one of the receiver ports 17 and 18and is positioned vertically relative to the receiver ports whereby thefluid jet 26 emerging from the nozzle crosses the gap L between thenozzle and receiver ports and impacts upon the opposite endwall 16 inposition to be divided equally between the two receiver ports 17 and 18in the absence of upward or downward acceleration of the device 11.Since the fluid jet 26 travels in a substantially horizontal direction,some downward deflection of the jet 26 occurs in passage across the gapL due to gravity. This may be compensated for by situating thecenterline 27 of nozzle orifice 23 at a level higher than that of thepoint of tangency 28 of the receiver ports 17 and 18, the amount of thisdisplacement D being determined by the length of the gap L and the jetvelocity. Gravitational drop may also be compensated for by directingthe centerline 27 of nozzle orifice 23 slightly upward relative tohorizontal.

Accordingly, in the absence of upward or downward acceleration of thedevice 11, the fluid jet 26 from nozzle 22 is received by ports 17 and18 and divided equally therebetween. Thus, in the absence ofacceleration, equal flows and equal pressures occur in the two outletpassages 19 and 21. Should the device 11 be accelerated upwardly,inertial effects cause the fluid which is travelling across the gap L tolag begind such motion and the point of impact of the jet 26 on receiverendwall 16 is displaced towards port 18. Under this condition, fluidflow and pressure in outlet port 21 rises while the flow and pressure inport 19 drops by an amount dependent on the extent of the jet deflectionand thus on acceleration rate. Accordingly, a fluidic signal indicativeof acceleration is produced which may be used to indicate suchacceleration or to actuate mechanism as will hereinafter be described.

Conversely, if the device 11 undergoes downward acceleration, inertialeffects on the jet 26 cause the flow and pressure in outlet port 19 torise while the flow and pressure in outlet passage 21 drops. Thus, thedevice 11 produces a fluidic signal indicative of acceleration in eitherthe upward or downward direction and such signals are distinguishablefrom each other.

The output signals thus generated by the device 11 may be caused toactuate an acceleration indicator or may be transmitted to an analyzinginstrument or may be amplified and used to actuate mechanism which is tobe operated in the presence of acceleration. One example of a mechanismof this kind is depicted diagrammatically in FIG. 1. Specifically, avehicle wheel 29 and certain elements of the wheel suspension 31 areshown wherein mechanism controlled by the device 11 acts to reduce roadshocks which may occur if the wheel passes over an obstacle such as alarge rock 32.

Referring to FIG. 1, fluid under pressure is supplied to the nozzle 22from a suitable reservoir 33 by a first pump 34. As the device 11operates from inertial effects on the jet 26, it is usually preferableto employ a heavy hydraulic fluid such as oil, for example, to enhanceresponse although it will be apparent that pneumatic fluids may beemployed if desired. A relief valve 36 is connected between the outletof pump 34 and reservoir 33 to maintain a constant predetermined outletpressure. The pressurized fluid from the outlet of pump 34 istransmitted to the nozzle supply passage 24 of the device 11 through acompensator valve 37 which will hereinafter be described in more detail.

While the signals generated in output passages 19 and 21 may be ofsufficient strength for direct utilization in some instances, it isfrequently necessary that such signals be amplified. In this example,two stages of amplification are provided by first and second fluidicproportional amplifiers 38 and 39 respectively. Amplifier 38 may be ofthe known form having a supply port 41 which is connected to the outputof pump 34, and having a pair of control ports 42 and 43, which areconnected to receiver passages 19 and 21 respectively of device 11, andfurther having a pair of output ports 44 and 46 and a vent port 47. Thesecond stage amplifier 39 may be of the same form and has a supply port48 connected to the outlet of pump 34, a pair of control ports 49 and 51respectively connected to output ports 44 and 46 of amplifier 38, a pairof output ports 52 and 53 and vent port 54. At any given time, apressure and flow differential is present between the output ports 52and 53 of amplifier 39 which is proportional to the pressure and flowdifferential at receiver ports 17 and 18 of device 11 but thedifferential is of substantially greater magnitude and thus is morereadily capable of operating mechanisms which are to be actuated in thepresence of acceleration. As previously described, this pressure andflow differential is normally zero but in the presence of upwardacceleration of device 11, pressure and flow at amplifier output 52rises while the pressure and flow at output 53 decreases in an amountwhich is a function of the rate of acceleration. A reversed change ofpressures and flow at the two amplifier outlets 52 and 53 occurs in thepresence of downward acceleration of the device 11.

Considering now one example of mechanism which may be controlled by theacceleration signals from amplifier output ports 52 and 53, the vehiclewheel suspension system 31, may consist of a strut 56 having a pivotconnection 57 to a frame member 58 of the vehicle and which extendsbackward from the pivot connection. The wheel 29 may be attached to thevehicle through an axle 59 journaled in a rearward portion of the strutwhereby the wheel is able to pivot upward and downward relative to thevehicle frame while passing over irregularities such as rock 32. Tomaintain in the wheel 29 at a normal level relative to frame 58, asuspension spring 61 may be disposed between the strut 56 and vehicleframe 58. As is well understood in the art, such a resilient suspensionaids in reducing the transmission of road shocks to the frame of thevehicle 58 does not wholly eliminate undesirable upward and downwardmotion of the vehicle frame. The present suspension system further aidsin reducing upward and downward motion of the frame 58 under suchconditions by means of a double acting hydraulic jack or cylinder 62coupled between the frame member 63 and the back end of strut 56 throughpivot joints 63 and 64 respectively. Cylinder 62 is proportioned so thatthe piston 66 thereof is normally centered within the cylinder by spring61 when the vehicle is traveling on a smooth surface. The ports 67 and68 of cylinder 62 are, except under conditions to be hereinafterdescribed, intercommunicated through a flow restriction 69 in a cylindercontrol valve 71 and thus the cylinder normally provides a shockabsorber effect by dampening but not prohibiting pivoting movement ofthe strut 56 and reduces oscillation of the strut and wheel from energystored in spring 61 following such pivoting.

Pressurized fluid for operating the cylinder 62 is provided fromreservoir 33 by a second pump 72 having a pressure relief valve 73connected to the outlet thereof to maintain a constant outlet pressure.Control valve 71 has a pair of ports 74 and 76 respectively connected toports 67 and 68 of the cylinder 62 and has an additional pair of ports77 and 78 respectively connected to pump 72 and reservoir 33. Valve 71is spring biased to a normal position at which ports 77 and 78 areblocked while ports 74 and 76 are communicated through the flowrestriction 69 as previously described. Application of fluid pressure toa first pilot means 79 urges the valve toward a second position at whichport 77 is communicated with cylinder port 68 while drain port 78 of thevalve is communicated with cylinder port 67 thereby tending to contactthe cylinder and to pivot strut 56 and wheel 29 upward relative to frame58 while compressing the spring 61. Application of fluid pressure to anopposite pilot means 81 of valve 71 acts to urge the valve towards athird position at which supply port 77 is communicated with cylinderport 67 while cylinder port 68 is communicated to drain port 78 therebyextending the cylinder 62 to pivot strut 56 and wheel 29 downwardlywhile distending spring 61.

Pilot means 79 and 81 of the control valve are connected to outputs 52and 53, respectively, of the second stage fluidic amplifier 39.Accordingly, in operation, any initial upward motion of the wheel 29 issensed by device 11 and amplified by amplifiers 38 and 39 causing thepressure at valve pilot means 79 to rise while the pressure at pilotmeans 81 decreases. Control valve 71 is thereby shifted towards thefirst position at which high pressure fluid is transmitted to cylinderport 68 while the opposite cylinder port 67 is vented. The resultantcylinder contraction forcibly drawn the wheel 29 closer to vehicle frame58 enabling the wheel to override the obstacle 32 without imparting aviolent upward motion to the vehicle frame. When upward motion due tothe obstacle 32 ceases, the fluid pressures at pilot means 79 and 81again equalize and valve 71 is returned to the normal position at whichspring 61 may restore the wheel 29 and piston 66 to the normal positionsrelative to frame 58.

Should the wheel 29 drop into a sudden depression in the underlyingsurface, an opposite operation occurs. Device 11 senses the initialdownward motion causing an increased pressure to be applied to pilotmeans 81 while the pressure at pilot means 79 is decreased and valve 71therefore shifts towards the position at which cylinder 62 extends toforcibly lower the wheel 29 relative to frame 58. Thus the end effect ofthe system is to assist the wheel 29 to rise and drop substantiallyindependently of vehicle frame 58 as necessary to traverseirregularities in the underlying surface.

Analysis of the above-described system will show that precision ofoperation depends on the jet flow 26 of device 11 traversing the gap Lat a predetermined velocity and further depends on the gravity induceddrop of the jet in passage across the gap being of a constant amount.These two considerations are interrelated. If the jet velocity shoulddecrease, a longer time is required to cross the gap and thusgravitational drop will increase thereby disturbing the desiredrelationship between the amount of flow which enters the two receiverports 17 and 18. Basically, emission of the jet from nozzle 22 at aconstant velocity is provided for by the relief valve 36 which maintainsa constant output pressure from pump 34. However, the velocity of thejet 26 is sensitive to another factor, specifically the viscosity of thefluid and viscosity can be altered by ambient temperature changes orother factors. Another factor which could disturb the pre-establishedrelationship between the position of the receiver ports 17 and 18 andthe jet 26 is tilting of the device 11 away from a strictly horizontalplane. In certain applications, such as in the vehicle suspension systemdescribed above, such tilting can readily occur, since the vehicle maytravel on sloping terrain. When the device 11 is strictly horizontal,gravitational force acts on the jet 26 substantially at right anglesthereto and this is the condition for which the level of the receiverports 17 and 18 relative to nozzle 22 is preadjusted as previouslydescribed. If receiver end 16 of the device should then be tilted upwardrelative to the nozzle end 14, gravitational force then has a componentpulling backward on the jet as well as at right angles thereto and thustends to decrease jet velocity thereby causing more of the flow to enterlower receiver port 18 than enters upper receiver port 17. Conversely,should nozzle end 14 be tilted upward relative to receiver end 16,gravitational force has a component tending to accelerate the jet andthe result is that more of the flow will enter the upper port 17 thanenters the lower port 18. Thus, if uncorrected, tilting of the device 11would degrade the precision of the acceleration signals produced atreceiver passages 19 and 21.

Compensator valve 37 is provided to correct automatically for bothviscosity changes and tilting of the device 11 so that extreme accuracyin the acceleration signals is maintained. Compensator valve 37 has avalve body 82 with a bore 83 in which a spool 84 is slidable. A passage86 leading to bore 83 receives the fluid from pump 34 while a slightlyoffset outlet passage 87 transmits such fluid to the nozzle supplypassage 24 of device 11. Spool 84 has a central groove 88 with an edge89 for regulating the flow of such fluid to the device 11 in accordancewith the position of spool 84 in bore 83. A constricted flow passage 91at one end of bore 83 is connected to outlet port 44 of first amplifier38 while a similar constricted flow passage 92 at the other end of bore83 is communicated with outlet port 46 of amplifier 38.

If the jet flow 26 at device 11 divides evenly between receiver ports 17and 18, the output pressure from first amplifier ports 44 and 46 areequal and are transmitted to opposite ends of compensator valve spool 84to center the spool in bore 83 thereby causing a predetermined normalpressure to be transmitted to the nozzle 22 of device 11. Should lowerreceiver port 18 receive more flow than the upper receiver port 17 forany continued length of time, either from a viscosity related decreasein the volocity of the jet 26 or from an uptilting of end 16 of thedevice, amplifier 38 supplies a greater pressure to constricted passage91 of the compensator valve than is provided to the opposite constrictedpassage 92, and spool 84 is shifted a proportionate amount to increasethe fluid pressure at nozzle 22. This restores the desired equaldivision of flow between receiver ports 17 and 18. Similarly, shouldupper receiver port 17 receive more flow than lower receiver port 18 fora continued period because of a viscosity reduction or an uptilting ofend 14 of the device, than a greater pressure is supplied to compensatorvalve spool passage 92 while a lesser pressure is supplied to passage91. Spool 84 is thereby shifted to reduce the pressure at nozzle 22 torestore the desired relationship. The compensator valve 37 does notsignificantly counteract the desired acceleration signals because of thefact that the spool piloting passages 91 and 92 are constricted to blockrapid pressure changes from the spool. Thus the compensator valve cannotrespond to the brief pressure differentials at amplifier outputs 44 and46 which are generated by acceleration, but can only respond to the moreprolonged alteration of the jet 26 which occurs in the presence ofviscosity changes or tilting.

While the invention has been described with respect to a singleembodiment, it will be apparent that many variations are possible, andit is not intended to limit the invention except as defined in thefollowing claims;

What is claimed is:
 1. In a vehicle having a fluidic system disposed onsaid vehicle for detecting acceleration and for producing anacceleration signal in response thereto, the combination comprising:avehicle wheel, suspension means for attaching said wheel to said vehiclewhile providing for vertical movement of said wheel relative to saidvehicle, resilient means for exerting a force between said vehicle andsaid suspension means for urging said wheel towards a predeterminedvertical position relative to said vehicle, an extensible andcontractible fluid cylinder coupled between said vehicle and suspensionmeans, fluid flow receiver means having a first flow receiver port, anda second flow receiving port with the center of said second flowreceiving port being spaced apart from the center of said first flowreceiving port in the direction along which acceleration is to besensed, fluid jet forming nozzle means having a flow orifice, means forsupplying fluid under pressure to said nozzle means whereby a fluid jetis ejected therefrom, support means holding said nozzle means in aspaced-apart relationship from said receiver means with said jet beingdirected towards said receiver ports across an unobstructed gap, wherebydeflection of said fluid jet relative to said receiver means in responseto acceleration is accompanied by an increase of flow through one ofsaid ports and a decrease of flow through the other thereof, fluidicsignal output means communicated with said receiving ports forgenerating fluidic signals in response to brief departures of thepressure at said receiving ports from a predetermined value, a fluidpressure piloted cylinder control valve connected between said cylinderand a source of high pressure fluid and having a normal position atwhich said cylinder is isolated from said source of high pressure fluid,said control valve having a first pilot means for responding to arelative increase of fluid pressure at said first receiving port bysupplying high pressure fluid to said cylinder to raise said wheelrelative to said vehicle and having second pilot means responsive to arelative increase of fluid pressure at said second receiving port bysupplying high pressure fluid to said cylinder to lower said wheelrelative to said vehicle, and compensating means for varying the flowpassage to said jet nozzle to restore said receiver port pressures tosaid predetermined value in response to relatively prolonged departuresof said pressures from said predetermined value.